Brush clip assembly



Nov. 28, 1967 MEYER ET AL BRUSH CLIP ASSEMBLY Filed June 11, 1965 INVENfORS HERBERT H. MEYER ARCHIE R.K

BY M

IN SBURY f ATTORNEY United States Patent 3,355,611 BRUSH CLIP ASSEMBLY Herbert H. Meyer, Bay Village, Ohio, and Archie R.

Kingsbury, Keystone, S. Dak., assignors to Union Carbide Corporation, a corporation of New York Filed June 11, 1965, Ser. No. 463,275

' 8 Claims. (Cl. 310248) ABSTRACT OF THE DISCLOSURE 1 A brush clip assembly comprising a brush of the type conventionally employed in electrical devices such as motors and generators, and a non-metallic clip interlockingly secured to the brush to prevent wear thereto by accommodating a spring finger. The brush is provided with agroove confined. to a side surface thereof and having an opening in the top surface, and the clip is formed such that one segment is inserted into and extends along the groove and one segment extends across the top surface of the brush.

This invention relates to an electric brush and more particularly to an improved brush clip assembly.

A brush clip is a component which is attached to an electric brush of the type conventionally employed in certain electrical devices such as motors and generators. It is used to prevent wear of the brush by accommodating the spring finger or hammer and to act as a guide and is consequently often referred to as a hammer or finger clip.

A wide variety of clip configurations are available. In addition, several types of connections are presently used to secure the clip to the brush. A typical clip configuration and connection is that illustrated in Publication No. OBI-1961 published in October 1961 by the National Electric Manufacturers Association and referred to therein as A clip. This assemblycon sists generally of a metal strip bent so as to lie on top of the brush and connected to the side of the brush by. one or more rivets. This particular assembly generally includes a metal washer be tween the rivet head and the brush.

Several problems are often encountered in the production of this type of brush clip assembly. Spinning the heads on the rivet in order to get a tight connection is a delicate and difficult task even for the skilled artisan. In"addition,'breakage of the carbon or graphite brush sometimes occurs in the area of-rivet connection because the brush is weakened by the necessary assembly operations. Furthermore, once the metal clip is connected to the brush, subsequent loosening or breakage of the clip orbrush while in use could cause the metal clip to seri- 'ously damage the motor or generator in which it is functioning.

' Inorde-rto overcome these difliculties, several hammer clip connections whichdo not depend upon a rivet have been'advanc'ed but these connections generally are not satisfactory since they are not equipped to withstand vibration and shock under normal operating conditions. Further, .it is often thecase that these connectionsrnay not beadvantageously employed with split brushes.

' It is the principal" object of this invention, therefore, to provide an improved brush clip assembly.

A furtherv objectof this invention is to provide a brush clip assembly which does not depend upon a rivet or similar fastener to secure the clipto' the brush and yet 'may be readily employed with a split brush.

Still another object of this invention is to provide a brush clip assembly which is sturdy, inexpensive, and requires a minimum of skill to assemble.

Other objects and advantages of this invention will "ice become apparent from the following description taken in conjunction with the following drawing wherein:

FIGURE 1 is an isometric view of the brush clip assembly of the invention;

FIGURE 2 is an isometric view of a typical brush having a dovetailed groove therein.

FIGURE 3 is an isometric view of the brush clip assembly of the invention wherein a split brush is illustrated.

Broadly, the objects of the invention are accomplished by a brush clip assembly comprising a carbon or graphite or metal graphite brush having a groove machined in one side thereof, and a generally L shaped clip engaging the groove in such a manner as to be interlockingly secured to the brush. The extended portion of the clip is designed to extend parallel with the top surface of the brush and if desired beyond the width edge of the brush.

The bush clip assembly of the invention may best be described by referring to the drawing and particularly FIGURE 1.

In FIGURE 1 the carbon or graphite brush 10 has a groove 12 machined along the side surface 14. The groove begins at the top surface 16 which is opposite the con tact surface 18, and terminates at a determined distance from the top surface 'along the side surface 14 at point 20. A clip 22 is positioned within the groove 12. The clip preferably extends beyond the top surface 16 of the brush 10.

The groove 12 and the clip 22 are designed so that a secure connection exists between them when the assembly is made. This is accomplished by providing an in terlocking arrangement between clip and groove such as an interference fit relationship. As another example, the groove may be dovetailed, or undercut with a correspondingly shaped clip inserted therein. By way of illustration, a half inch wide clip is secured in the groove if an interference of 0.005 inch is provided.

FIGURE 2 illustrates a dovetailed groove 12 which may be employed in the assembly of the invention. It will be noted that the groove suitably extends into the top surface 16 of the brush a distance d which in all cases is equal to or greater than the thickness of the clip used.

Referring now to FIGURE 3, asplit brush comprises brushes 10 and 24. A clip 22 resides in the groove 12 (not shown) in brush 10 and extends beyond the top surface 16 so as to cover a portion of the top surface 26 of the brush 24. In this manner the clip 22 serves as a guide for brush 24 as well as accommodating the spring finger (not shown) to prevent wear of the brush.

To assemble the connection of the invention it is only necessary that the clip 22 be inserted into the groove 12 at the top 16 and a slight pressure he applied. To ensure tightness of fit at low brush surface temperatures, the clip width should be sufiiciently wide or of such edge angle as to provide initial interference upon insertion. Thus, costly, time consuming and undesirable steps, such as securing a rivet in place, are eliminated.

Although the clip may be composed of any suitable non-metallic material, it must be composed'of a material having a thermal coefficient of expansion-greater than that of the brush material. A plastic (or equivalent), clip material is advantageous because it can withstand the shock, vibration, and wear to which it is subjected, and it will not cause a short circuit or other electrical damage upon breaking since it is electrically non-conductive. In addition, when a split brush is used, the two brush halves Will conduct substantially the same current. This is believed to be due to the improved riding properties of the non-metallic clip whenlin contact with metal spring finger. Commutation will also be improved due to the resiliency of plastic or equivalent material. Several equivalent materials which may be used in the construction of the clip are elastomeric materials in general, polypropylene, nylon, Nylafil Teilon and fibre glass, and molded fibres as well as other similar materials.

To evaluate the effectiveness of the subject invention a series of tests were conducted. In the first test, several clips each having a configuration similar to that illustrated in the drawing but composed of three different materials i.e. polypropylene, Nylafil, and metal, were connected to identical brushes in an interference fit-dovetailed connection and the assemblies were subjected to severe vibration at extremely different temperatures utilizing conventional equipment. The results of this test are illustrated in Table I below. The second test involves a measurement of the currentdiiference between brushes in a split brush assembly comparing." a Nylafil clip in an interference tit-dovetailed connection: with a standard metal A clip? riveted split brush assembly. The test was run with two different levels of current i.e. 7-5 amperes and 175 amperes through the brushes. In. Table II, current flow out of the brushes is labeled Negative and current. flow into the brushes is labeled Positive.

TABLE L-VIBRATION 'nns r phere and thereby result in a greater bond between clip and brush. Furthermore, during operation the force -ot the spring finger or hammer on the clip is in such a direction as to force the clip down into the groove, once again resulting in a tighter and stronger connection.

It will be appreciated that a wide variety of alterations and modifications may be made without affecting the inventive concept of the assembly of the invention. For example, a small hole could be drilled near the bottom of the groove and the clip could be fpunched to form a dimple in the predrilled hole thereby giving a substitute or supplemental connecting characteristic to the assembly. As previously indicated, the preferred dovetail groove could be replaced by an undercut-groove and a correspondingly shaped clip. Although the clip is normally preformed and then inserted intothe groove it could be molded directly into the groove. Further, although the clip configuration illustrated herein is preferred, similar success may be accomplished if the clip is longer or shorter, wider or narrower, or is formed intoa larger or smaller angle. Better results are obtained it the-bottom Number vibrations, millions Material Clip temp.

Results Polypropyleneclips.-.

Assembly secure.

All clips-extremely loose.

l The same clips wereused ior'tliethree temperature tests.

TABLE II.-CURREN'I DIFFERENTIAL IN AM-PERES-LONG To SHORT wanna- 75 amps 175 amps Material Negative Positive Negative Positive No Difler'ence (amps) Difference (ampsl Ditference (amps) Difference (amps) readings .Aivg. Min Max. Avg. 3 M n. Max. Avg. Min. Max. Avg. Min. Max.

Std. Metal'nn. 37 1112 6 i 19.7 0 33.9 12' 41.7 4 70' Nylafll 157 6.9 0 16 I 151]; 2 24 20. 7 6 4'1 34.5 i 0 70 Table I shows that the assembly of the. invention will withstand extreme vibration. Furthermore, Table I illustrates that better results are obtained it the clips are composed of non-meta1lie materials such. as Nylafil' or polypropylene. In addition,v the assembly is virtually unaffected by' temperatures. far in excess of those which it will actually be subjected to; The data: in- Table II points out that the assembly of the invention will provide a superior current distribution between. brushes in a split brush" assembly.

It is important to note that the connection of the invention becomes stronger under normal operating conditions and this is contrary to the performance of prior art connections. The increase in strength-is due to the factthat the forces operating on the clip tendto augment the secure mechanical relationship of the clip and the groove. For example, since the clip is composed of a material. having a. higher thermal coefficient of expansion than the brush, it will expand during operation due to the heat rise in the surrounding equipment and atmos- Nylafi1-Registered trademark of Fiberfil Corporation, Warsaw, Incl, and the subject of U.S'. Patent No. 2,877,501- a combination of nylon and fibre glass.

"1efionReg'istered trademark of Du Pont Corporation a plastic consisting of a itetrutluoroethylene polymer.

of the clip is in: contact with the bottom of the groove since further support against shock and vibration. is then provided. I

What is claimed. is:

1. A brush clip assembly comprising at least. one brush,v said brush haing a. contact surface, a top surface opposite said contact surface, and a side surface between said contact surface and said top surface, saidbrush having a groove with an opening at said top surface and extending solely along said side surface; and a nonmetallic clip having a: coetficient of thermal expansion greater thanthat of said brush residing in said groove, said clip being so formed such that one segment thereof is inserted into and extends along said groove, and. one segment thereof extends across said top surface, said groove and said clip being structured such that said clip 6. The assembly of claim 1 wherein said clip is composed of Nylafil.

7. The assembly of claim 1 wherein said clip is composed of a plastic material.

8. A brush clip assembly comprising a first brush having a contact surface, a top surface opposite said contact surface, and a side surface between said contact surface and said top surface, said first brush having a groove with an opening at said top surface and extending solely along said side surface; a nonmetallic clip having a greater coefiicient of thermal expansion than that of said brush residing in said groove, said clip being so formed such that one segment thereof is inserted into and extends along said groove, and one segment thereof clip being structured such that said clip is interlockingly secured to said first brush; and a second brush electrically connected to said first brush and so positioned as to reside beneath at least a portion of said clip.

References Cited MILTON O. HIRSHFIELD, Primary Examiner.

extends across said top surface, said groove and said 15 D. F. DUGGAN, Assistant Examiner. 

1. A BRUSH CLIP ASSEMBLY COMPRISING AT LEAST ONE BRUSH, SAID BRUSH HAVING A CONTACT SURFACE, A TOP SURFACE OPPOSITE SAID CONTACT SURFACE, AND A SIDE SURFACE BETWEEN SAID CONTACT SURFACE AND SAID TOP SURFACE, SAID BRUSH HAVING A GROOVE WITH AN OPENING AT SAID TOP SURFACE AND EXTENDING SOLELY ALONG SAID SIDE SURFACE; AND A NONMETALLIC CLIP HAVING A COEFFICIENT OF THERMAL EXPANSION GREATER THAN THAT OF SAID BRUSH RESIDING IN SAID GROOVE, SAID CLIP BEING SO FORMED SUCH THAT ONE SEGMENT THEREOF IS INSERTED INTO AND EXTENDS ALONG SAID GROOVE, AND ONE SEGMENT THEREOF EXTENDS ACROSS SAID TOP SURFACE, SAID GROOVE AND SAID CLIP BEING STRUCTURED SUCH THAT SAID CLIP IS INTERLOCKINGLY SECURED TO SAID BRUSH. 